We posted a PDF version of the patterns and practices guidance release, Developing Applications for SharePoint 2010.  This guidance will really help you understand the architecture and development decisions for SharePoint 2010 custom application development, and has rich code examples as well as a reusable library.  The MSDN release is available at www.microsoft.com/spg, and the PDF version can be downaloed from codeplex at http://spg.codeplex.com.  Please provide feedback either through my blog, on the discussion forums of the Codeplex site, or you can directly email me at ckeyser@microsoft.com.